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Bore Measuring Accuratly -Throw away the gauges !

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  • Bore Measuring Accuratly -Throw away the gauges !

    I didn't want to bust into the current thread on telescopic gauges, so started a new thread
    http://bbs.homeshopmachinist.net/thr...ings-questions

    I was kidding about throwing away your measuring tools, but serious about getting accurate measurements.
    I have used and taught my method for many years and it is simple , accurate, and even displays errors in the bore.
    Better yet you use only one mike and that is the same mike generally used for the mating part, so you eliminate another error possibility

    Just use a GOOD Adjustable Parallel gauge in your bores.
    Insert it in the bore and expand it until all 4 corners are in firm contact with the bore walls.
    Use your OD Mike on the opposite corners to measure the Bore.
    The adjustable parallel will also tell you if the bore is tapered because you can wiggle one end and which end is larger. Even the slightest taper is exposed !
    Also it is then easy to rotate the Parallel to see if the bore is egg shaped. ( remeasure !)

    Cheap parallel gauges do not work !
    You want the same sharp or controlled corners on the gauge consistently and a smooth slide function.
    The condition of the dovetails is also a must.

    Hope this helps
    Rich
    Green Bay, WI

  • #2
    I had never thought of that technique, it took a couple of minutes to twigg what you meant by opposite corners.
    There's only one problem for me, I don't have any!
    If you used a depth mic on the overlap, having preset the diameter, it might be a useful variation in certain circumstances.
    Last edited by old mart; 05-01-2018, 11:55 AM.

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    • #3
      Hi Rich,
      I did not find any useful hits searching for parallel bore gauge.
      Can you post a link to a picture?
      Thanks

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      • #4
        Originally posted by wombat2go View Post
        Hi Rich,
        I did not find any useful hits searching for parallel bore gauge.
        Can you post a link to a picture?
        Thanks
        Also called adjustable parallels.
        https://www.amazon.com/Starrett-S154.../dp/B0006J4EAC

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        • #5
          There is a variety of those where the surfaces are rounded so they measure without fussing to get all the edges to touch. Should be easier to use for bores
          CNC machines only go through the motions

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          • #6
            Funny thing is that as a youth that had just started using my Father's lathe and so I had an inkling of it all was my Dad doing an important internal bore for a heated/cooled shrink fit on a large ring. He measured the shaft with the fancy 0-6" mic set that I still have and then did the bore using a set of simple outside spring calipers that used the threaded shaft and thimble. He checked for a rubbing fit as he swept one of the legs back and forth axially for the sort of feel he was after. Then he would replicate that feel on the mic. It was winter so the next evening he put the shaft outside to cool (no beer fridge in his shop) and heated up the collar. It slipped on over the shaft with almost no persuasion and when it cooled down it was solid as it would be if welded. It was something in the neighbourhood of 4 to 5 inches as I recall.

            And now we have telescoping gauges, inside micrometer sets and now this rather clever trick of using adjustable parallels. All this to replace the skill and feel of the old world machinists that kept their inside and outside spring calipers close to hand.

            Just for giggles one day I'm going to make a fairly large bore that still is within range of my telescoping gauges and then try the spring caliper trick to see if I can match the measurement and what it takes to do so.
            Chilliwack BC, Canada

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            • #7
              Originally posted by BCRider View Post
              And now we have telescoping gauges, inside micrometer sets and now this rather clever trick of using adjustable parallels. All this to replace the skill and feel of the old world machinists that kept their inside and outside spring calipers close to hand.
              None of those tools are really "new". Seems the only difference is that in our shops we have cheaper versions of tools that might have only been in a machinists toolbox.
              I don't dispute that using the adjustable parallels in place of a telescoping gage is clever. But I don't doubt that the use of parallels to measure a round bore also exists as a machinist's kink in some book published nearly a hundred years ago.

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              • #8
                Ok, Here are some photos showing how the Adjustable Parallel is set and measured.
                Note, you must measure the diagonal corners !

                Rich

                Green Bay, WI

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                • #9
                  Thanks for the pics, now I understand the diagonal measurement.

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                  • #10
                    Nice one! Thanks for sharing!
                    Andy

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                    • #11
                      Damn so simple and it never occurred to me !
                      They are a favorite for me for measuring slots.. quick and fast. . And accurate.

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                      • #12
                        One thing they will NOT do, and telescoping gages WILL do, is check the amount of taper in a bore.

                        Aside from that, they work fine.
                        Last edited by J Tiers; 05-02-2018, 02:10 AM. Reason: spelling
                        CNC machines only go through the motions

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                        • #13
                          I think that telescoping gauges were made so that you could check the bore wear in an IC engine cylinder, below the unworn ring at the top. I don't think anything else does this.
                          'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                          • #14
                            Originally posted by Richard P Wilson View Post
                            I think that telescoping gauges were made so that you could check the bore wear in an IC engine cylinder, below the unworn ring at the top. I don't think anything else does this.
                            There are measuring "sleds" made specifically o do that.... to check the wear, the change in measurement along the bore, but maybe not the actual measurement

                            For measuring the acual size, you need the telescoping gage, or other bore gage. Don't tell AKB... he says they will year up the bore and plow a groove in the crosshatching.
                            CNC machines only go through the motions

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                            • #15
                              Bore comparator?
                              Mark

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